The present invention relates to an image pick-up apparatus for a facsimile equipment, phototelegraphic apparatus or the like and more particularly to an improved image pick-up apparatus including a transversely extending photo sensor having a length corresponding to the width of an original and an optical system comprising an array of lenses.
To facilitate understanding of the present invention it will be helpful that a typical conventional image pick-up apparatus of the above-mentioned type will be briefly described with reference to FIG. 1 which illustrates the apparatus by way of a perspective view with both the side walls removed therefrom. As will be apparent from the drawing, the image pick-up apparatus includes light sources 31 and 32, a lens array 20 constituting an optical system for building an image and a photo sensor 10 in the form of an elongated sensor each of which is housed in the space as defined by upper and lower casings PA and PB. The photo sensor 10 is dimensioned to have a length corresponding to the width of an original manuscript OR placed on the upper casing PA and is constructed by a combination of a base board 11, a required number of divided electrodes 12 arranged on said base board 11, a layer of photoconductive film 13 made of such materials as amorphous silicon, Selenium-Tellurium (Se-Te) and organic semiconductor coated over said divided electrodes 12 and a layer of light transmissive common electrode 14 coated over the whole surface of said photoconductive film 13. Namely, the photo sensor 10 is constructed by a large number of photoelectric converting elements arranged across the full width of the original manuscript OR with an arrangement density normally in the range of 8 to 12 pieces/mm for a single picture element, each of said photoelectric converting elements comprising a single divided electrode 12, a part of the photoconductive film 13 and a part of the common electrode 14.
From the viewpoint of designing the image pick-up apparatus in possibly small dimensions the photo sensor 10 requires an optical system by means of which an image is built without any enlargement or reduction, i.e., an image on the original manuscript OR is built on the photo sensor 10 at a dimensional ratio of 1 : 1. To meet the requirement, the lens array 20 is provided above the photo sensor 10 as illustrated in FIG. 1. The lens array 20 is generally constituted by so-called beam condensing optical fibers. For instance, the lens array 20 is constructed in such a way that the beam condensing optical fibers 21 are arranged side by side with the same arrangement density as that of the photoelectric converting elements or with an arrangement density higher than the latter within a suitable holder in such a posture as illustrated in FIG. 1 in which its optical axis is directed substantially at a right angle relative to the original manuscript OR placed on the upper casing PA.
The light sources 31 and 32 are symmetrically disposed at both sides of the lens array 20 so as to emit light beams toward the original manuscript OR through slits 33 and 34 formed on the light sources. Further, a glass plate 90 is fitted into a recess on the casing PA while it extends in the transverse direction over a distance corresponding to the width of the original manuscript OR, so that light beam is emitted in the direction as identified with an arrow mark F1 from each of the light sources 31 and 32 toward the original manuscript OR movably placed on said glass plate 90.
After light beam coming from the light sources 31 and 32 is reflected at the original manuscript OR, it advances down toward the lens array 20 in the direction as identified with an arrow mark F2 and passes through the latter. Thereafter, it advances down further toward the photo sensor 10 in the direction as identified with an arrow mark F3. It should be noted that scanning of an image on the original manuscript OR is carried out by successively driving the photoelectric converting elements in the photo sensor 10.
Since the conventional image pick-up apparatus is constructed in the above-described manner, there is generally established the following dimensional relation as shown in equation (1) between a distance LA measured from the lower surface of the original manuscript OR down to the inlet surface of the lens array 20 and a length LB of the lens array 20 in consideration of the influence of many factors such as diameter of fluorescent lamp for the light sources 31 and 32, position of the slits 33 and 34, i.e., entrance angle of light beam to the original manuscript OR, optical properties of the lens array 20 and others. EQU LB=2LA (1)
Further, the substantially same dimensional relation is established between a distance LC measured from the outlet surface of the lens array 20 down to the inlet surface of the photo sensor 10 and the aforesaid length LB of the lens array 20. Accordingly, the total distance LT measured from the lower surface of the original manuscript OR down to the inlet surface of the photo sensor 10 can be represented by the following equation. ##EQU1##
Assuming that LA is, for instance, 12 mm, it results that LT becomes 48 mm. In view of practicability about 50 mm will be required for the total distance LT.
This means that a distance between both the upper and lower casings PA and PB is enlarged, resulting that the whole structure of the image pick-up apparatus must be unfavorably designed in larger dimensions. For instance, in case of a facsmile equipment the above-described image pick-up apparatus is utilized in an original read-out section but it is difficult to design and construct the whole apparatus in smaller dimensions due to the fact that other auxiliary apparatuses such as original recording section or the like are additionally attached to the image pick-up apparatus. As is well known, recent accelerated spread of so-called office automation machines throughout a variety of industries causes necessity for mounting them in a narrow space at a high functional efficiency from the viewpoint of maneuverability and operative efficiency and therefore requests for designing them in compact dimensions have been raised from many users.